1. Technical Field
The present invention relates to a MOSFET.
2. Related Art
Conventionally, a transistor is formed by epitaxially growing gallium nitride (GaN) on top of a sapphire substrate, as shown in Patent Document 1 and Non-Patent Document 1.    Patent Document 1: Japanese Patent Application Publication No. 2008-243927    Patent Document 1: Semiconductor Science and Technology 25 (2010) 125006 (14 pp)    Non-Patent Document 2: 1.8 mΩ·cm2 vertical GaN-based trench metal-oxide-semiconductor field-effect-transistors on a free-standing GaN substrate for 1.2-kV-class operation, Applied Physics Express 8 054101 (2015)
When a channel formation region is formed of GaN in a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the actual threshold voltage (Vth) is lower than the setting value thereof. Furthermore, when the channel formation region is formed of GaN, there are cases where the actual carrier mobility (μ) during the ON state is lower than the setting value thereof. The reason for the actual threshold voltage (Vth) and the actual carrier mobility (μ) being lower than the setting values is unknown.